1) Field of the Invention
This invention relates generally to a metal diaphragm valve which can be used in the fluid pipings of semiconductor producing equipment, and more particularly to such a device of micronized build, with small-diameter fluid passages.
2) Description of the Prior Art
There has been increased demand for micronized metal diaphragm valves for use in the fluid pipings of semiconductor manufacturing machines. As illustrated in FIG. 2, such a valve 20' consists a domed diaphragm 1 made of elastic metal material which is normally upwardly urged to bulge away from an annular valve seat 4 (as shown by broken line), that is mounted below the diaphragm, encased in a cylindrical casing 2. A valve drive system 3 is operatively connected to the diaphragm 1, and is operated to push a reciprocating piece 3a that is centrally mounted in the casing 2. The piece 3a, when depressed by the valve drive 3, physically exerts pressure on the diaphragm 1, and causes it to cave in and is brought into contact with the seat 4 below. When the diaphragm 1 is pressed sealingly against the seat 4, fluid-flow relationship is shut down between an inlet passage 10 and an outlet passage 13 that is formed below the casing 2.
When the drive system 3 releases the pressure on the reciprocating piece 3a, the diaphragm 1 retracts back, on its own elasticity, to the original convex position depicted by broken line in the drawing, thereby establishing fluid-flow relationship between the inlet passage 10 and outlet passage 13.
In conventional technologies, the annular valve seat 4 are fixedly secured, or caulked, in position in the casing bed 5 with a pair of annular collars 4a along both inner and outer circumferences of the seat. This caulking with collars, however, make the bed 5 irregular and bumpy in the surface, increasing a risk of stagnation of fluid in an area surrounding the ribbed valve seat 4, technically referred to as "dead zone".
Metal diaphragm valves have to be build small where they are used in the fluid pipings of semiconductor chip manufacturing equipment. In this application, their annular beds 5 have to have a sufficiently wide flat surface between the outer collar 4a and the inner walls of the casing 2, to remove the possibility of developing stagnation of fluid because of dead zone, when the diaphragm 1 is actuated to its opening position. As a result, after the diaphragm is fully closed, part of the fluid is left unevacuated. This undrained fluid leads to inefficient valve operation. Moreover, attempts at replacing fluid are often aborted since part of the fluid will refuse to leave the region of dead zone.
When the valve is built small as for the fluid piping of IC-chip assembling machines, the annular casing bed cannot be made to sufficiently wide because of technical difficulty. Grinding applied to the collar 4a has tended to leave metal particles or excessively polished patches to ruin the sealing capacity of the seat 4. Using multiple-stage electropolishing, an efficient technique to obtain a fine surface, is also be limited because of the narrow bed surface of the collars 4a.